Gonadal hormones and sex differences in nonreproductive behaviors in rodents: organizational and activational influences

Responses to novelty stress in female F344 rats: effects of age and d-fenfluramine treatment

To elucidate some of the mechanisms underlying the neuroendocrine and neurochemical changes associated with age in female rats, we administered the serotonin (5-HT) releaser and reuptake inhibitor, d-fenfluramine (d-FEN; 0.0 or 0.6 mg/kg/day, PO) for 30-38 days to young (4 month) and old (21 month) F-344 female rats. Animals were placed into a novel open field (OF) for 20 min before sacrifice. Control animals were sacrificed immediately upon removal from their home cage (HC). Old rats exhibited significantly (p < 0.05) less exploratory behavior and a smaller CORT response to OF than young animals. d-FEN treatment had no effect on plasma ACTH and CORT levels or exploratory behavior. The old HC rats had significantly (p < 0.05) higher plasma levels of prolactin (PRL) than the young HC rats. A stress induced increase in PRL secretion was observed in the old rats only, which was attenuated by d-FEN treatment. In the OF groups, both the young and old rats showed elevated medial frontal cortex (MFC) dopamine turnover (DOPAC/DA ratio), but only the young rats exhibited an elevation in norepinephrine (NE) turnover (MHPG/NE ratio). d-FEN treatment blocked the stress-induced increase in NE turnover in the young rats and the increase in DA turnover in the old rats. These data suggest that 5-HT activity could be involved in the age-related changes in the MFC catecholamine and PRL responses to stress in female rats.

Contribution of stress and gender to exploratory preferences for familiar versus unfamiliar conspecifics

An apparatus for measuring the exploratory preferences of rats for familiar and unfamiliar conspecifics in a novel environment was designed. The exploratory behavior of males and females was compared and contrasted to that elicited in response to an acute aversive event. Sprague-Dawley male and female rats were exposed to restraint and 60, 1 s, 1 mA tailshocks and returned to their home cage. Either 2 or 24 h later, they were placed in a novel environment with a familiar cage-mate and an unfamiliar conspecific of the same sex. Relative to unstressed controls and females, males stressed 2 h previously decreased the exploration of the unfamiliar conspecific, exhibiting a rapid decrease over the course of the trial. In response to the stressor, however both sexes, however, decreased the exploration of the familiar conspecific, decreased their overall activity, and returned preferentially to their starting quadrant. None of these stress-induced effects were evident 24 h later upon the first or second exposure to the apparatus. Thus, exposure to the stressor transiently increased perseveration and decreased activity in males and females, but only decreased the exploration of novel conspecifics in males. These results indicate that a number of behavioral responses to stressors are conserved across gender, but those relating to novelty are more pronounced in males.

Expression of early genes in estrogen induced phenotypic conversion of neuroblastoma cells

Estrogens are known to modulate the growth rate and differentiation state of a number of cells. In uterine, as well as in mammary tumor cells, estrogen-dependent proliferation and differentiation are correlated to a series of biochemical responses, including increased expression of proto-oncogenes such as: c-fos, c-jun and c-myc. Since estrogens were shown to regulate the proliferation and the differentiation state of cells of nervous origin, the aim of the present study was to investigate whether these effects were associated to changes in the expression of early genes. In the model system utilized, the human cell line SK-ER3, an increase in c-fos mRNA and Fos protein without change of c-jun and related genes mRNA concentration was observed after short term treatment with 17 beta-estradiol (E2). A significant decrease of c-fos, c-jun and jun-D proto-oncogene mRNA levels were found after prolonged hormonal treatment. The exposure to the hormone did not determine any change in N-myc expression. Since the three protooncogene mRNAs are rapidly induced following estrogen treatment in other cell systems and target tissues, it is concluded that the estrogen-induced differentiation of neuroblastoma cells is correlated to a pattern of expression of early genes that might be peculiar for the activity of this hormone in neural cells.

Gender differences in the effects of haloperidol on avoidance conditioning in mice

Gender differences in the effects of haloperidol (0.075 mg/kg per day for 5 days) on avoidance conditioning were evaluated. We also studied performance of the subjects free of the drug and the acute effects of haloperidol in animals trained without drug 48 h after the last haloperidol administration. Latencies of escape and avoidance responses, number of nonresponses, escapes, avoidances, crossings during the adaptation period, crossings during intertrial intervals, and total crossings per minute were analyzed. This dosage impaired conditioning of the male animals but did not attain the same effects on females. Haloperidol did not deteriorate performance of the task when it had been learned previously without drug. The results confirm the existence of gender differences in haloperidol effects on avoidance conditioning in mice and suggest that these differences are related to the learning process and not only to the impairment of motor behavior characteristic of neuroleptic drugs.

Postischemic cerebral blood flow recovery in the female: effect of 17 beta-estradiol

Female reproductive hormones are considered to be protective agents in atherosclerotic vascular disease and stroke. The present study determined if there are unique cerebrovascular responses in female animals to global cerebral ischemia and if 17 beta-estradiol is important to postischemic outcome in brain. Three groups of anesthetized, sexually mature rabbits were treated with normotensive four-vessel occlusion (6 min) and 3 h of reperfusion: females chronically instrumented with 17 beta-estradiol implants (EFEM; n = 8, plasma estradiol level = 365 +/- 48 pg/ml), untreated females (FEM; n = 8, estradiol = 13 +/- 3 pg/ml), and untreated males (M; n = 8, estradiol < limit of radioimmunoassay). CBF (microspheres) and somatosensory evoked potential (SEP) amplitude were measured during ischemia/reperfusion. Baseline hemispheric blood flow and regional flow distribution were not altered by chronic estradiol treatment. Hemispheric blood flow was equivalently reduced during ischemia in FEM and M (6 +/- 1 and 9 +/- 2 ml min-1 100 g-1, respectively); however postischemic hyperemia was greater in FEM than M (CBF = 257 +/- 27 and 183 +/- 27 ml min-1 100 g-1. However, EFEM experienced higher CBF during ischemia (e.g., 13 +/- 2 ml min-1 100 g-1) and less hyperemia (134 +/- 4 ml min-1 100 g-1 in hemispheres) in numerous brain regions than FEM. CBF at 3 h reperfusion was not different among the groups. Recovery of SEPs was incomplete and similar in all groups. We conclude that chronic exogenous 17 beta-estradiol treatment increases CBF during global incomplete ischemia and ameliorates postischemic hyperemia in the female animal.

Progesterone releases dopamine in male and female rat striatum: a behavioral and microdialysis study

1. The acute effect of progesterone at a physiological dose (50 micrograms) was investigated behaviorally by measuring postural deviation of rats bearing a unilateral lesion of the entopeduncular nucleus and biochemically by in vivo microdialysis in the striatum. 2. Ovariectomized female and intact male rats displayed a significant increase of postural deviation to the lesioned side 30-65 min after the subcutaneous injection of progesterone with a return to control values thereafter. 3. In addition, rats of both sexes had increased dopamine (DA) in the first 20-40 min dialysate collection following the progesterone injection. The metabolites of DA dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the dialysate were also increased after the progesterone injection and HVA levels remained elevated for a longer time than DA, up to 120 min after progesterone. 4. Progesterone, at a physiological dose and independently of estrogens can therefore rapidly increase DA release in the striatum of rats of both sexes as revealed in vivo behaviorally and biochemically.

A multivariate assessment of spontaneous locomotor activity in the Mongolian gerbil (Meriones unguiculatus): influences of age and sex

A multivariate assessment of the spontaneous locomotor activity of male and female Mongolian gerbils (Meriones unguiculatus) was obtained using a Digiscan automated animal activity monitoring system. Spontaneous motor activity data were collected over 1 h (5-min samples) for groups of male and female gerbils ranging from 26-341 days of age (26, 38, 62, 116, 151, 172, 196, 247, and 341). Variables examined included: total distance travelled, average distance per movement, average speed, number of horizontal movements, time in horizontal movement, time per horizontal movement, number of vertical movements, time in vertical movement, and time per vertical movement. Age had a significant effect on spontaneous activity; all measures of horizontal activity increased from preadulthood (26 and 38 days) and remained relatively constant thereafter for adults (62+ days). Vertical activity (rearing) measures were found to increase from the 62-day-old group to the 151- and 172-day-old groups and then decrease among the older groups (196+ days). Across the 12 samples, within sessions, all horizontal and vertical activity measures (except average speed) declined for both males and females. Habituation was more rapid for the preadults than for the adults on all horizontal measures except average distance per movement. No consistent sex differences in locomotor activity were found.

Sex differences and the effect of gonadectomy on morphine-induced antinociception and dependence in rats and mice

1. Differences between sexes and the effect of bilateral surgical gonadectomy on the response to morphine analgesia and dependence were examined in rats and mice. 2. The analgesic response to morphine (5 mg/kg) was assessed by the hot plate and the abdominal constriction tests. Dependence was induced by injecting morphine at increasing doses (5-160 mg/kg) for 6 consecutive days and withdrawal signs elicited by injecting naloxone (2.5 mg/kg). 3. The base line reaction times in the intact control, sham-operated and gonadectomized animals of either sex were not significantly different from each other. 4. After treatment with morphine, the percentage increase in the reaction time in gonadectomized male and female rats and in gonadectomized male mice was significantly higher than in their respective controls. 5. The increase in the reaction time, after morphine treatment, was significantly higher in gonadectomized female rats than in gonadectomized male rats. 6. Naloxone-induced withdrawal signs in morphine-dependent gonadectomized rats and mice were not significantly different from those in sham-operated controls. However, female rats in both groups exhibited a significantly higher number of escape jumping responses than males.

Effects of neonatal ethanol exposure on saccharin consumption

Prenatal ethanol exposure has been associated with alterations in a variety of sexually dimorphic behaviors in rats. This study examined the effects of neonatal ethanol exposure on saccharin consumption, a sexually dimorphic behavior in rats. Subjects were Sprague-Dawley rats that were artificially reared (AR) from postnatal day (PN) 4-PN12 through gastrostomy tubes with ethanol exposure limited to PN4-PN10. The AR groups included two ethanol doses (6 g/kg/day and 4 g/kg/day) and an isocaloric maltose-dextrin control. A sham surgery control group was also included. The AR subjects were returned to their dams on PN13. At 21 days of age, subjects were housed with one same-sex sibling and free access to rat chow and water until testing. Subjects were tested for saccharin preference and consumption at 110 days of age. Typically, male rats consume less saccharin than females, and this was evident in the 4 g/kg ethanol group and both control groups. However, this was not apparent among the 6 g/kg ethanol-exposed males. Furthermore, saccharin preference seemed to be reduced in the females exposed to 6 g/kg ethanol. These data suggest that the "sensitive period" for ethanol's effects on sex differences in saccharin consumption extends into postnatal life.

Distribution of NMDAR1 receptor subunit mRNA and [125I]MK-801 binding in the hypothalamus of intact, castrate and castrate-DHTP treated male rats

This study examines NMDAR1 receptor subunit mRNA expression and [125I]MK-801 binding in hypothalamic and limbic nuclei of intact, castrate and castrate-dihydrotestosterone propionate (DHTP)-treated male rats. In intact rats, the highest levels of NMDAR1 mRNA were observed in the supraoptic, suprachiasmatic, ventromedial and arcuate nuclei. Low levels of hybridization were observed in the bed nucleus of the stria terminalis, lateral preoptic area, lateral hypothalamic area and lateral septum. In castrated rats both NMDAR1 mRNA and [125I]MK-801 binding are significantly decreased in the lateral septum compared to castrate rats treated with DHTP, a non-aromatizable androgen. NMDAR1 mRNA was also significantly decreased in the supraoptic nucleus of castrate rats when compared to castrate rats treated with DHTP. These data suggest that androgens may modulate NMDA receptor function in some parts of the central nervous system.

Effects of estradiol on radial arm maze performance of young and aged rats

Gonadectomized male and female Sprague-Dawley rats, given estradiol (E2) via sc Silastic capsules that generated proestrus levels of hormones, were tested for spatial memory performance on an 8-arm radial maze. Performance of males, with or without E2, exceeded that of females, with or without E2, for choice accuracy parameters over 20 trials. In addition, males reached criterion earlier than females (6 vs 11 trials). There were no significant effects of E2 on performance of either sex. When a 1-h delay was instituted between the 4th and 5th choices, the performance of males remained better than that of the females, and E2 administration was associated with a small, but significant, improvement in performance of the males but not the females. E2 administration to 25-month-old males also did not affect performance in regular trials, but performance was enhanced in trials with delays of 1-3 h after the 4th choice. These results show that estradiol can influence spatial memory performance and suggest that E2 may be beneficial for age and/or disease-related memory impairments.

The effects of acute and chronic cocaine administration on paced responding in intact and gonadectomized male and female Wistar rats

Intact and gonadectomized male and female Wistar rats pressed a lever on a multiple (tandem Random-Interval 30-s, Differential Reinforcement of High Rate 0.5-s) (tandem Random-Interval 30-s, Differential Reinforcement of Low-Rate 5.0-s) schedule of reinforcement. The pacing requirements maintained high and low response rates under equal reinforcement frequencies. Low doses of cocaine (1 and 3 mg/kg) either did not affect or slightly increased high and low response rates of intact and gonadectomized female rats, while they did not affect or decrease high and low response rates of intact and castrated male rats. Higher doses of cocaine (up to 30 mg/kg) dose-dependently decreased both high and low response rates for all subjects. Intact male rats were less sensitive to the rate-decreasing effects of these doses of cocaine than castrated male rats or intact and ovariectomized female rats. Chronic cocaine administration consistently resulted in behavioral sensitization only in intact male subjects. The results of this experiment provide further support for the notion that the behavioral effects of psychomotor stimulant drugs are not necessarily rate dependent but may depend upon the extent to which schedule contingencies allow for behavioral variability without negatively affecting behavioral outcomes.

Reduction of rat pup ultrasonic vocalizations by the neuroactive steroid allopregnanolone

Several of the recently characterized neuroactive steroids have been proposed to have anxiolytic effects in behavioral models when subjects were tested as adults. In this experiment, the effects on infant subjects were examined using the isolation distress model of anxiety. The production of ultrasonic vocalizations in week-old rat pups after maternal separation was assessed after ICV injections of vehicle or allopregnanolone (1.25-5 micrograms), or sham injections. Subjects were also observed for activity and behavioral responses and tested on three measures of sedation. Allopregnanolone caused a dose-dependent decrease in ultrasonic vocalizations, with increasing motor incoordination, ataxia, and turning at the higher doses. Sex differences were not observed for any measure. These results suggest the GABAA receptor binding site for neuroactive steroids is behaviorally active in neonates as well as in adults, and that the anxiolytic effects of the neuroactive steroids at this site may be dissociable from their sedative effects at low doses.

Decreased postnatal testosterone and corticosterone concentrations in rats following acute intermittent prenatal hypoxia without alterations in adult male sex behavior

The prenatal and postnatal testosterone surges in the male rat are associated with neurobehavioral sexual differentiation of the brain. Both surges can be attenuated by maternal stress or other environmental factors that activate the maternal and/or fetal hypothalamic/pituitary/adrenal (HPA) axis during the last week of gestation. Since hypoxia is known to activate the HPA axis, we studied its effect during gestation on sexual differentiation in the male rat. We examined the influence of intermittent hypoxic exposure during gestation with respect to the postnatal testosterone surge and corticosterone levels, and subsequent development of adult reproductive and nonreproductive sexually dimorphic behaviors. Plasma testosterone and corticosterone concentrations of male neonates were measured after maternal exposure to acute, intermittent, prenatal hypoxia (9% O2 6 h/day from Day 15 to 21 of gestation). Relative to normoxic controls, acute, intermittent, prenatal hypoxia significantly attenuated the postnatal testosterone surge. Postpartum plasma corticosterone levels in these animals were also suppressed. In adulthood, prenatally hypoxic animals exhibited normal masculine sex behavior. Lordosis behavior in response to estrogen and progesterone priming was not significantly different between treatment groups. Saccharin preference, a nonreproductive, sexually dimorphic behavior, was not significantly influenced by prenatal hypoxic exposure. These results demonstrate that in the male acute intermittent prenatal hypoxia attenuates the postnatal testosterone surge. However, this reduction failed to result in significant alterations in the expression of sex related behaviors in adulthood.

Interactions between 5-hydroxytryptamine (5-HT) and testosterone in the control of sexual and nonsexual behaviour in male and female rats

Two 5-hydroxytryptamine2 (5-HT2) agents, ritanserin and 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane HCl (DOI) (both at 0.25 mg/kg IP), were administered to castrated males bearing graded testosterone implants (empty, 2.5-, 5-, and 10-mm length) and to normal and neonatally androgenized ovariectomized females bearing 10-mm testosterone implants. The results indicate that testosterone stimulates male sexual behaviour and appears to have a dose-related anxiolytic effect, but no effect on other nonsexual activities. 5-HT and testosterone had opposite effects on male sexual behavior, with ritanserin (5-HT antagonist) enhancing activity in both sexes and DOI (5-HT agonist) inhibiting behaviour in males, the latter being testosterone-dependent. Independent of testosterone, ritanserin reduced locomotion and exploration and increased anxiety in males, while DOI increased locomotion and exploration in both sexes. Ritanserin had a gender-specific effect on anxiety which was independent of testosterone, since in castrated males it was anxiogenic whether they bore testosterone implants or not, while in females it was anxiolytic whether the female were neonatally androgenized (250 micrograms/pup testosterone proprionate [TP] on day 1) or not. These results show that 5-HT and testosterone have opposite effects on male sexual behaviour and these may be interrelated. In adulthood, their effects on nonsexual activities are not inversely related and are independent of each other in contrast to the relationship seen in the neonatal period.

Progesterone effects on the acquisition of conditioned avoidance responses an other motoric behaviors in intact and ovariectomized rats

This study demonstrates a significant impairment in the acquisition of conditioned avoidance responses in female rats during their estrus phase. Progesterone (PROG 5 mg) injected 6 h prior to the test, significantly enhanced the performance exhibited by rats at estrus, but not at diestrus. In ovariectomized rats, the acquisition of conditioned avoidance responses was similar to the exhibited during diestrus and this behavior was depressed by a single dose of estradiol benzoate (EB 2 micrograms) injected 48 h prior to the test. PROG antagonized the avoidance depression induced by EB, but it was not able to induce changes in the acquisition of conditioned avoidance response in ovariectomized rats without EB pretreatment. Estradiol appears to be the principal ovarian steroid modulating the acquisition of an avoidance task, whereas PROG seems to have a secondary role in this behavior, regulating the actions of estradiol on the brain. PROG failed to induce consistent changes in some spontaneous motor behaviors in intact and ovariectomized rats.

Prenatal ethanol exposure: effects on androgen and nonandrogen dependent behaviors and on gonadal development in male rats

Prenatal exposure to alcohol may impair gonadal and behavioral development in male rats, possibly via reduction of perinatal androgenization. We examined locomotor activity on postnatal day 18 (PND 18), which is not influenced by perinatal androgens and juvenile play and testicular development (testes weight), which are dependent on perinatal androgen exposure, in rats whose dams consumed ethanol during pregnancy. Male offspring of pair-fed and lab chow-fed dams served as controls. Despite reduced anogenital distance at birth, indicating compromised perinatal androgenization, fetal ethanol-exposed males did not exhibit demasculinization of play behavior. Hyperactivity in fetal ethanol-exposed males indicated that the treatment regimen was sufficient to produce behavioral deficits. Testes weight was reduced in both ethanol-exposed and pair-fed offspring, indicating that nutritional deficits associated with maternal ethanol intake may impair normal gonadal development in male rats. The findings suggest that fetal ethanol exposure may influence gonadal development but not necessarily affect a gonadal hormone-dependent behavior.

Androgen regulation of adrenocorticotropin and corticosterone secretion in the male rat following novelty and foot shock stressors

To examine mechanisms responsible for sex differences in hypothalamo-pituitary-adrenal (HPA) axis responsiveness to stress, we studied the role of androgens in the regulation of the adrenocorticotropin (ACTH) and corticosterone (CORT) responses to foot shock and novelty stressors in gonadectomized (GDX) or intact male F344 rats. Foot shock or exposure to a novel open field increased plasma ACTH and CORT, which was significantly greater in GDX vs. intacts. Testosterone (T) or dihydrotestosterone propionate (DHT) treatment of GDX animals returned poststress levels of ACTH and CORT to intact levels. Estrogen treatment of GDX males further increased poststress CORT secretion above GDX levels. There was no difference in the ACTH response of anterior pituitaries from intact, GDX, and GDX+DHT animals to CRF using an in vitro perifusion system. There were no differences in beta max or binding affinity of type I or II CORT receptors in the hypothalamus or hippocampus of intact, GDX, or GDX+DHT groups. These data demonstrate an effect of GDX on hormonal indices of stress. The increased response in GDX rats appears to be due to the release from androgen receptor mediated inhibition of the HPA axis. This inhibition by androgen is not due to changes in anterior pituitary sensitivity to CRH, nor to changes in type I or type II corticosteroid receptor concentrations.

Sex differences in anxiety behavior in rats: role of gonadal hormones

These experiments examined the role of gonadal hormones at both the organizational and activational time periods on sex differences in plus-maze behavior. In the first experiment, adult female Long-Evans rats were found to spend more time on the open arms of the plus maze than adult males, indicating less anxious behavior. In the second experiment, male and female subjects received a neonatal treatment (chemical castration with flutamide or tamoxifen, vehicle injection, or no injection) and a prepubertal treatment (gonadectomy, sham surgery, or no surgery). Adult females receiving either neonatal tamoxifen or prepubertal ovariectomy spent less time on the open arms than control females, but females who received both treatments were the most defeminized subjects. Males were not affected by the absence of gonadal hormones at either time period. These experiment indicate that female gonadal hormones play an important role both organizationally and activationally in plus-maze behavior. The role of the GABA receptor complex in mediating this effect is discussed. Knowledge of sex differences in plus-maze behavior may help to make this maze a more useful tool in investigating anxiety behavior in rats.

Sex differences and stress response of WKY rats

Wistar Kyoto (WKY), Fischer-344 (F-344), and Wistar male and female rats during either proestrus-estrus or diestrus phases of the estrus cycle were exposed to the ulcerogenic procedure of water restraint. Both male and female WKY rats revealed significantly more stomach ulcers as compared to Wistar and F-344 rats of the same sex. No persistent sex difference was observed, but ulcer severity was more pronounced during the proestrus-estrus phase as compared to the diestrus phase of the estrus cycle particularly in WKY female rats. In the second study, WKY females were observed as more active in the open-field test (OFT), but more immobile in the forced swim test (FST), as compared to WKY male rats. In addition, proestrus-estrus WKY females were less active in the OFT and significantly more immobile in the FST as compared to diestrus females. Thus, proestrus-estrus WKY females were judged as more emotional in the OFT and as exhibiting more signs of behavioral depression according to the FST. These studies suggest that the steroid hormone milieu in WKY rats may be responsible for these behavioral changes as well as the stress responsiveness in this stress-susceptible rat strain.

Altered adult sexual behavior in the male rat following chronic prenatal hypoxia

The last week of gestation is a critical period for the sexual differentiation of the brain in the rat. Exposure to prenatal stress during this period has been shown to demasculinize and/or feminize adult male sexual behavior. Many of the neurochemical and endocrine responses to hypoxia are similar to that observed under stressful conditions such as restraint stress. Therefore, we examined the postnatal consequences on reproductive and nonreproductive sexually dimorphic behaviors in male offspring of dams exposed to chronic hypoxia during the last week of gestation. In addition, we examined sensorimotor development in offspring of both sexes. Pregnant Sprague-Dawley dams were exposed to continuous hypoxia (10.5% O2 from gestational day 15 to 21). Offspring were weaned at 22 days of age and group housed. Behavioral tests were conducted with littermate representatives. In adulthood, male rats prenatally exposed to hypoxia had significantly delayed initiation latencies of masculine sexual behavior and decreased number of ejaculations, but did not display a significant increase in feminine sex behavior potentials. Developmentally, animals exposed to prenatal hypoxia did not differ significantly from controls with respect to day of eye or ear opening, or the in times of righting reflex, negative geotaxis or cliff avoidance. Wire hanging latencies in hypoxic exposed animals were significantly greater than controls around the time of eye opening, but did not differ at earlier or later ages. A significant effect of hypoxia was detected on stride length at 95 days of age, but other aspects of gait patterns were similar to controls. No group differences in gait patterns were observed at 17 or 45 days of age. In addition, no significant differences were observed in open field activity, circadian locomotor activity, saccharin preference, or Morris water maze test. This hypoxia regimen did not influence the occurrence of the prenatal or postnatal surge of plasma testosterone. Overall, these results provide some evidence that, in males, mild, chronic prenatal hypoxia may result in incomplete masculinization of adult reproductive behavior in the absence of overt changes in perinatal testosterone surges.

Predator-induced opioid and non-opioid mediated analgesia in young meadow voles: sex differences and developmental changes

The present study examined developmental changes in the nociceptive responses of male and female meadow voles, Microtus pennsylvanicus, exposed to a garter snake, a natural predator of young voles. After 15 min of exposure to the presence of a garter snake, neonatal-juvenile voles (5-20 days of age) displayed naloxone (1.0 mg/kg)-sensitive opioid mediated analgesic responses, while after a brief 30-s exposure to the snake, voles displayed a higher amplitude, non-opioid analgesia that was insensitive to naloxone and blocked by the serotonin-1A (5-HT1A) agonist, 8-hydroxy-2-(di-n-propylamino)tetralin. The levels of opioid and non-opioid mediated analgesia declined during development as the threat presented by the snake decreased. Young female voles also displayed a significantly greater non-opioid, 5-HT1A sensitive analgesia than males, with no significant sex differences in the lower amplitude opioid analgesia. These results indicate that young (neonatal) meadow voles that are exposed to a naturally threatening stimulus display sexually dimorphic analgesic responses. These findings also illustrate the need to consider the ecological context when examining environmentally-induced analgesia.

Sensation seeking in opposite-sex twins: an effect of prenatal hormones?

Intrauterine hormones and position with respect to male and female littermates influence sexually dimorphic adult behavior in litter-bearing animals. Opposite-sex dizygotic twins offer the opportunity to examine analogous effects on sex-related human behaviors. To illustrate this approach, Sensation Seeking Scale (SSS) scores from 422 British twin pairs, including 51 opposite-sex pairs (Zuckerman, M., et al., J. Consult. Clin. Psychol. 46:139-149, 1978), were reanalyzed. Zuckerman et al. (1978) have shown that some aspects of sensation seeking are consistently increased in males relative to females. In comparing age-adjusted data for opposite and same-sex twins, our reanalysis demonstrated the predicted increase in sensation seeking in female members of opposite-sex pairs. Results were significant for measures of disinhibition, experience seeking, and overall sensation seeking. In contrast, male opposite-sex twins were not significantly different from male same-sex twins. Although psychosocial explanations of the increased sensation seeking in opposite-sex female twins cannot be excluded, these finding are consistent with hypothesized in utero hormonal influences on later behavioral development.

A mechanism for virilization of female spotted hyenas in utero

Female spotted hyenas exhibit male-like genitalia and dominance over males. Hyena ovarian tissues incubated in vitro produced large quantities of the steroid hormone precursor androstenedione. The activity of aromatase, which converts androstenedione to estrogen, was one-twentieth as great in hyena versus human placental homogenates. In comparison, the activity of 17 beta-hydroxysteroid dehydrogenase, which converts androstenedione to testosterone, was equal in the two homogenates. The limited aromatase activity may allow the hyena placenta to convert high circulating concentrations of androstenedione to testosterone, which results in virilization of the fetal external genitalia and possibly destruction of fetal ovarian follicles. Androstenedione production by residual ovarian stromal cells during reproductive life accounts for the epigenetic transmission of virilization in female spotted hyenas.

Sex differences and gonadal hormones influence susceptibility to the activity-stress paradigm

The present study investigated the effect of gonadal hormones on activity, food consumption, severity of ulceration, weight loss, and survival duration in male and female rats exposed to the activity-stress (A-S) paradigm. Animals received either sham surgery or gonadectomy and were housed in activity wheels or standard suspended cages. Results indicated that gonadectomized animals were more likely to engage in high running levels in the A-S paradigm; in addition, castrated males developed significantly more ulceration than the other groups. Neither sex nor gonadectomy affected the survival duration of A-S animals.

Female circulating sex hormones and hippocampal sympathetic ingrowth

Following cholinergic denervation of the hippocampal formation, via medial septal (MS) lesions, sympathetic fibers, originating from the superior cervical ganglia, growth into the hippocampus. Previous studies have demonstrated a sexually dimorphic effect of this neuronal rearrangement on recovery of a spatial-learning task, with this rearrangement being detrimental in male but protective in female rats. Circulating male sex hormones were found to interact with this effect in male animals. In this study we assessed the role of circulating female sex hormones on the behavioral and biochemical effects of hippocampal sympathetic ingrowth (HSI). For the behavioral studies female rats underwent either sham ovariectomy (sham OVARX) or OVARX and were taught a standard radial-8-arm maze task. Following attainment of criterion, animals underwent one of three surgical procedures: sham surgery; MS lesions+sham ganglionectomy (MS); HSI group; MS lesions+ganglionectomy (MSGx). As in our previous study, animals with HSI (i.e. MS group) were found to recover learning faster (in fact, these animals did not differ from controls) than animals with MS lesions without HSI. Gonadal status did not affect this behavioral recovery. For the biochemical studies hippocampal norepinephrine (NE) and choline acetyltransferase (ChAT) were measured in animals sham OVARX and OVARX, 8-12 weeks after the neurosurgical procedure. MS lesions (i.e. MSGx; MS) were found to reduce ChAT activity, regardless of circulating sex hormones. In controls NE levels were similar between OVARX and sham OVARX. NE levels were markedly elevated in the OVARX MS group compared to all other groups including sham OVARX. In the MSGx groups, NE levels were reduced compared to controls, while comparisons between these groups revealed a significant reduction in NE levels in the OVARX MSGx group compared to sham OVARX MSGx group. These studies suggest that female circulating sex hormones interact with brain injury in a very complex manner. However, this interaction does not appear to mediate the changes in behavior observed after HSI.

Stimulus characterization of estradiol applying a crossfamiliarization taste aversion procedure in female mice

In female mice (n = 240), the estradiol stimulus was characterized by studying preexposure effects of sex steroids and sickness-inducing drugs on estradiol-induced (50 micrograms/kg SC) conditioned taste aversion (CTA). It was established that preexposure to estradiol itself (2-50 micrograms/kg SC) attenuates the development of CTA produced by the hormone. Only partial crossfamiliarization effects were found with progesterone (50-200 micrograms/kg SC) and testosterone (250-1000 micrograms/kg SC), steroids that induce CTA themselves. Preexposure to the sickness-inducing drugs lithium chloride (22 mg/kg SC) and apomorphine (0.1-0.2 mg/kg SC) prevented or substantially reduced the development of estradiol-induced CTA, respectively. It was concluded that only a low degree of stimulus resemblance exists between estradiol and the other principal sex steroids, progesterone and testosterone. In addition, it was concluded that the estradiol stimulus resembles the stimuli produced by sickness-inducing drugs.

Annual variations in the vasopressin neuron population of the human suprachiasmatic nucleus

The mammalian suprachiasmatic nucleus is considered to be the major component of the biological clock, involved in the temporal organization of a wide variety of physiological and behavioral processes. The present study was conducted to investigate whether there are diurnal or annual variations in the morphology of the vasopressin-containing neuron population of the suprachiasmatic nucleus in human beings. To that end, the brains of 48 human subjects were investigated. A marked annual variation was observed in the volume and vasopressin cell number of the human suprachiasmatic nucleus: the volume of the vasopressin cell population was, on average, 2.5 times larger in October-November than in May-June and contained 2.7 times as many vasopressin-immunoreactive neurons. In general, the annual cycle of the human suprachiasmatic nucleus showed a non-sinusoidal pattern with a maximum in early autumn, a lower plateau in winter and a deep trough in late spring and early summer. In contrast, no such seasonal variations could be detected in suprachiasmatic nucleus vasopressin numerical cell density or cell-nuclear diameter. The number of vasopressin-immunoreactive neurons in the paraventricular nucleus of the hypothalamus, on the other hand, did not show any significant periodic changes over the year, indicating the specificity of the suprachiasmatic nucleus rhythm. In contrast with the annual cycle of the suprachiasmatic nucleus, no significant diurnal variations were observed in any of these parameters. In conclusion, the findings indicate that photoperiod may be considered a potential environmental factor controlling the activity of the vasopressin system of the human suprachiasmatic nucleus.

Neonatal exogenous testosterone modifies sex difference in radial arm and Morris water maze performance in prepubescent and adult rats

To study the involvement of testosterone in the development of spatial abilities, testosterone propionate (TP) was administered to male and female rats during the first week after birth. As adults, these rats were trained and tested on the radial arm maze (RAM) or the Morris water maze (MWM). Sex and neonatal TP treatment influenced number of trials to criterion, accuracy, and the use of an adjacent-arm strategy on the RAM, as well as the speed with which the rats learned the location of a hidden platform in the MWM. On both RAM and MWM, control males performed better than control females, but TP treatment reversed this pattern, producing better maze performance in females and worse in males. Neonatal TP effects on MWM performance were also examined in 21-day-old male and female rats. Performance paralleled that of the adults in all but the testosterone-treated male group, which did not differ from control males. The results of this study provide support for the hypothesis that circulating testosterone during brain development may play a role in the development of spatial memory, and suggest that, in the rat, both the sex difference and testosterone influence are present early in life.

Early postnatal estrogen organizes sex differences in the extinction of a CRF running response

In the present study the organizational effects of sex steroids on the sexually dimorphic extinction of a continuously food-rewarded running response were investigated. Gonadally intact female rats neonatally treated from day 1 to day 8 of the postnatal life with estradiol benzoate (EB), dihydrotestosterone (DHT) or vehicle, and males treated in the same period with the antiandrogen ciproterone acetate (AC), the estrogen antagonist tamoxifen (TX) or vehicle were studied in adulthood during the acquisition and extinction phases of the response in a short and narrow runway. No difference in performance between groups was obtained in the response acquisition. However, during extinction control males extinguished faster than control females. DHT treatment to females and neonatal CA administration to males had no effect on the expression of sexual dimorphism. Conversely, TX administration to the males increased male's resistance to extinction at the levels shown by control or DHT females, whereas the females treated with EB exhibited similar extinction rates to those observed in nonhormonal treated or CA males. This finding suggests that the organizational effect of testosterone on the sexually dimorphic behavior studied in the present report are mediated by testosterone conversion to estradiol throughout the aromatization pathway in the brain.

Chin-marking behavior in male and female New Zealand rabbits: onset, development, and activation by steroids

Chin marking (chinning) frequency was determined daily in 25 male and 24 female New Zealand rabbits aged 31-150 days. Chinning appeared earlier in females (mean +/- SD = 41 +/- 16 days) than in males (47 +/- 13 days). Between days 30-50, females displayed chinning more frequently than males. Thereafter, chinning increased steadily in both sexes up to day 100. Chinning curves levelled on days 100 and 140 in males and females, respectively. Profile analysis of male and female chinning curves showed significant differences in their slopes and in their population means (p < 0.001). At 7 months of age (days 210-224), both sexes displayed adult chinning frequencies: mean of means +/- SD = 103 +/- 18 and 79 +/- 14 marks/10 min in males (n = 8) and females (n = 8), respectively. The administration of testosterone propionate (TP, 1 mg/day) or estradiol benzoate (EB, 1 microgram/day) to males and females, respectively, from days 31-50, stimulated higher chinning frequencies than those displayed by untreated animals. Results suggest that chinning frequency increases throughout development largely as a consequence of a concomitant increase in sex steroid secretion.

Testosterone as appetitive and discriminative stimulus in rats: sex- and dose-dependent effects

Stimulus properties of subcutaneously injected testosterone were studied in male and female rats. In a conditioned place preference procedure, dose-dependent effects (doses: 0, 0.5, and 1 mg/kg) were observed in males. In females, no place preference could be established (doses: 0, 1, and 3 mg/kg). In addition, 1 mg/kg testosterone acquired discriminative stimulus control in male rats in a taste aversion procedure. Animals injected with this hormone prior to saccharin-LiCl pairings and with its vehicle prior to saccharin-NaCl pairings suppressed fluid intake following the administration of testosterone and not following the administration of the vehicle. Subsequent generalization tests revealed dose-dependent stimulus control of this hormone (range of substitution doses: 0.125-2 mg/kg). It is concluded from the results that at least pharmacological (supraphysiological) doses of testosterone may act as appetitive stimuli in male rats, but not in female rats. Furthermore, in male rats (pharmacological doses of) testosterone also possess discriminative stimulus properties.

The effect of prenatal ethanol exposure on scentmarking in the C57BL/6J and C3H/He mouse strains

In utero exposure to ethanol has been shown to alter sexually dimorphic behaviors in rats. However, it is not clear whether this phenomenon is robust in other species, such as the mouse, which is sensitive to ethanol-induced birth defects. Further, it is not known whether significant differences exist across murine strains. If similar to the classic teratogenic effects of ethanol, it would be expected that strain differences in sensitivity should be evident, with some strains demonstrating an alteration in sexually dimorphic behavior and other strains demonstrating little or no effect. As a first attempt to address these issues, we have examined two mouse strains widely used in prenatal alcohol research, the inbred C3H/He and C57BL/6J strains. Scentmarking was selected as the behavior of interest. It is robustly sexually dimorphic in the rat and mouse, with males marking more than females and preliminary reports have demonstrated that in utero ethanol exposure reduces this behavior in the male rat. In the mouse strains selected for study, pregnant females were provided with either a liquid diet consisting of 25% ethanol-derived calories or pair-fed an isocaloric liquid diet from gestation days 6-18. An additional control group was included which was fed laboratory chow ad lib throughout gestation. Male and female offspring of each strain were tested for scentmarking at 65-75 days of age. As expected, results showed that the effect of prenatal ethanol exposure on scentmarking varied with both strain and sex. In the C3H/He strain, scentmarking was reduced significantly in male ethanol-exposed offspring (i.e., the males were feminized).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of early postnatal sex steroids on acquisition and extinction of a continuously reinforced lever-pressing response

The effects of early postnatal dihydrotestosterone (DHT) and estradiol on the sexually dimorphic continuously reinforced lever-pressing response were investigated. 90-day-old male rats postnatally treated (during the first eight days of postnatal life) with cyproterone acetate (CA), tamoxifen (TX) or vehicle, and 90-day-old females treated with estradiol benzoate (EB), DHT or vehicle in the same postnatal period, were studied during the acquisition and extinction of the continuously reinforced lever-pressing response using a free-operant procedure. During acquisition, the control males made more responses per minute than the control females, and also reached the extinction criterion significantly sooner than the females. CA treatment impaired the male's performance at the levels of that shown by females, whereas TX treatment affected neither acquisition nor extinction. Inversely, in both experimental phases females treated with DHT performed like control females, whereas the acquisition and extinction performances of the EB-females were similar to those obtained in the control or TX male groups.

Seasonal changes in the suprachiasmatic nucleus of man

The mammalian suprachiasmatic nucleus (SCN) is considered to be the principal component of the biological clock, generating a wide variety of physiological and behavioral circadian rhythms. In addition to its implication in circadian rhythms, the SCN is also involved in the expression of some seasonal cycles. In the present study we show that the volume of the human SCN and the number of vasopressin-immunoreactive neurons contained within it fluctuate significantly over the year, with values being about twice as high in the autumn as in the summer. In contrast, no seasonal variations could be detected in the paraventricular nucleus (PVN), another major vasopressinergic cell group in the hypothalamus. The present findings suggest that the human SCN is influenced by seasonal variations in photoperiod.

Variation in maternal care and individual differences in play, exploration, and grooming of juvenile Norway rat offspring

Individual differences in two different forms of maternal licking, time in nest and nursing, were measured during the first 2 weeks after birth. Two treatments were imposed to reduce maternal anogenital licking (AGL): peripheral zinc sulfate to interfere with reception of pup chemosignals, and dietary saline to reduce appetite for pup urine. Both treatments reduced AGL but did not affect other maternal licking. Zinc sulfate was more effective than saline during the first week, but was somewhat less selective as it also increased time in nest. Selected behavioral patterns were measured in male and female juveniles and related by multiple regression to the behavior of their mothers. Independent of the method of manipulation, maternal AGL was a significant predictor of play and open-field defecation males and of some forms of activity in the open field in both sexes. The relationships between other maternal variables and juvenile behavior were more modest. These data demonstrate that intervening in the sensory regulation of maternal behavior can produce predictable changes in stimulation provided by the dam, thereby providing a useful means for investigating the effects of protracted differences in early stimulation in otherwise normal developmental contexts.

Testosterone improves maze performance and induces development of a male hippocampus in females

In a combined behavioral and morphometric study, we observed a testosterone-related sexual dimorphism in the granule cell layer of the hippocampus of Sprague-Dawley rats that appears to be related to sex differences in spatial performance. This cell layer was larger and laterally asymmetrical in males. Neonatal testosterone treatment of females resulted in a more male-like hippocampus. These treated females also performed better than controls, and as well as males, on a spatial navigation task. In addition, a strong correlation between the size of granule cell layers and maze performance was detected.

Behavioural effects in adulthood of neonatal manipulation of brain serotonin levels in normal and androgenized females

5HT concentrations in the hypothalamus are higher in females than males over the second week of life and this differentiation is testosterone-dependent. We have investigated the possible influence of 5HT over this period on the development of systems that control adult behaviour, in particular those influenced by neonatal testosterone. Neonatal androgenization (250 micrograms/pup testosterone propionate; TP; on day 1 postpartum) induced a masculine pattern of behaviour in females ovariectomised in adulthood and bearing a TP implant. The neonatal treatment reduced exploration, motor activity and female sexual behaviour and increased anxiety, orientation toward the incentive female and male sexual behaviour. Depletion of 5HT by pCPA (100 mg/kg days 8-16 postpartum) enhanced the TP-induced increment in locomotion and female sexual behaviour and increased sexual orientation toward the incentive female, while 5HTP (20 mg/kg days 8-16 postpartum) antagonised the reduction in exploration by TP. Thus 5HT may normally exert an inhibitory control on the action of neonatal testosterone on exploration, motor activity and sexual behaviour. Neonatal PCPA treatment also had a marked anxiolytic effect which was independent of the presence of T as it was noted in normal and androgenized females and previously has been observed in intact males. This might indicate a primary control by a serotonergic system on the development of the systems controlling anxiety.